I am sorry that I didn't make the term metadata clear. What I want is actually the time when the data uploaded by specific users was downloaded and edited. Thank you very much for your kind reminding.
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YvanJan 31 '12 at 18:15

For inspiration, check out the blog posting "OpenStreetMap: a Year of Edits" by Derick Rethans (http://drck.me/osmyoe11-9nz). He discusses how he got hold of the changes in the OSM data set that happened in 2011 and how he made a beautiful video out of it. Intrigued to learn what use you are investiging!

Thank you very much for your answers. But what I really mean about the term metadata is data about data which can be information about contributors who upload and edit the map. And here what I specially concern about is the time data which describes the uploading, editing and downloading time of the data. Still, as an OSM newie, I have been benefited a lot from your answers about vector data retrieving techniques.
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YvanJan 31 '12 at 18:22